The regulation of FasL expression -: A distinguishing feature between monocytes and T lymphocytes/NK cells with possible implications for SLE

Monocytes and lymphocytes from patients with systemic lupus erythematosus (SLE) had a higher cell surface expression of Fast than the corresponding cells from healthy individuals. Inhibitors of metalloproteases upregulated the surface expression of Fast in peripheral blood lymphocytes (PBL), indicating that a metalloprotease is responsible for the cleavage of FasL. The level of sFasL in serum was slightly increased in the patient group compared to the controls. Therefore, the possible contribution of various mononuclear cell types to the release of Fast was analyzed. Isolated NK cells and T lymphocytes released Fast into the medium and the release was prevented by inhibitors of metalloproteases. In contrast, isolated monocytes did not release Fast. FasR expression was elevated in patients with inverted CD4/CD8 ratio, while Fast expression showed no relationship to CD4/CD8 ratio. The absence of Fast release by isolated cells and a high level of surface expression of Fast distinguish monocytes and T lymphocytes/NK cells.